This invention relates to methods for tendering using a uniquely designed semi-submersible tender adapted for facilitating servicing of offshore oil and natural gas production platforms, subsea wells, and other subsea infrastructure in water depths up to 10,000 feet.
The present invention specifically relates to methods for tendering using a semi-submersible tender, wherein the tendering occurs with different types of production platforms, such as a tension leg platform (TLP), a deep draft caisson vessel (SPAR), a fixed platform, a compliant tower, another semi-submersible production vessel, or a floating vessels.
The method of the present invention uses the uniquely design semi-submersible tender to moor safely floating production platforms in water depths exceeding several hundred feet for long periods of time, where the tender and tendering operations are subjected to weather ranging from a 1-year storm to a 10-year storm and up to a 100-year hurricane type.
It is very expensive to provide a production platform with adequate space for all the drilling and completion equipment needed to safely drill and complete a well, as well as, store drilling and completion equipment and materials in an environmentally conscientious manner, including drilling and completion risers, casings, tubings and drilling and completion fluids. Tenders have often been called into service to provide the required space needed on a rig and/or platform during the initial drilling and completion phase of an oil lease. Problems have traditionally existed in that most tenders cannot be kept alongside a platform in a constant spaced relationship during extreme weather without colliding with the platform. Specifically, tenders have not been able to remain in a connected capacity and avoid the risk of collision. Most commercial tenders cannot provide a high operational weather window to the tender and rig, and still endure the environmental load of up to a 10 year storm. See U.S. Pat. Nos. 4,065,934, and 4,156,577, which are hereby incorporated by reference on currently known tenders for production platforms. Most tenders have to be completely towed away to a safe location in the case of a tropical storm or extreme weather, which causes considerable expense to the drilling contractor and/or customer.
The need has long existed for methods of tendering a semisubmerisble which is safely moored in water depths exceeding several hundred feet for long periods of time, time exceeding one year, wherein the tender and tendering operation can be subjected to at least a 10 year storm and up to a 100 year storm, such as a hurricane season.
The present invention relates to a method for using a semisubmersible tender that provides up to 25,000 square feet of additional deck space and over 8000 barrels of liquid storage capacity for a production platform which enables the semisubmersible tender to keep a constant distance from a production platform while synchronizing to the low and mean movement frequencies, and to follow the mooring watch pattern of the production platform, such as a figure eight pattern, or an elliptical pattern, and to sustain, without damage, the environmental load of wind, current and wave forces of a 100-year cyclonic storm (such as a hurricane) in the 100-year extreme weather standby position, and up to a 10-year storm in a tendering position.
The invention includes a method for using a semi-submersible tender and an at least 6-point mooring system in deep-water for production platform to assist in the drilling of wells, well completion steps, and recovery of oil and gas in severe weather conditions.
The invention relates to a method of using a semi-submersible tender, wherein the tender has a deck, a shape that results in a combined environmental load less than 1000 kips in a 100-year extreme weather condition, a plurality of supports each with a rounded shape connected to the deck, a plurality of pontoons connecting the supports with each pontoon being capable of ballast transfer, wherein the tender is used for mooring in a tendering position relative to an offshore platform during a 1-year, 10-year, and 100-year storm, as well as non-storm conditions, using hawsers with adequate elasticity to accommodate the wave frequency between the platform and the tender and adequate stiffness to synchronize the mean/low frequency movement between the platform and the tender under an environmental load produced during a 10-year winter storm, and enough slack during a 10-year storm to enable the tender to move to a tender standby position, and wherein the tender uses an at least 6-point mooring system for creating global equilibrium between the platform and the tender.